Coastal groundwater dynamics with a focus on wave effects

Abstract

Groundwater dynamics in the coastal unconfined aquifer is one of the most important physical factors in the coastal zone since it greatly influences the nearshore hydrodynamics and beach morphodynamics, as well as interactions between oceanic and inland water systems. A solid understanding of the groundwater behavior in the coastal area is necessary for maintaining efficient coastal water management and supporting sustainable social-ecological development. Coastal unconfined aquifers are complicated while active systems in response to multiple oceanic forces such as tides and waves in various spatiotemporal scales, which have been evaluated and investigated over the last few decades. The present paper provides a comprehensive review of current understandings and advances in groundwater dynamics in coastal unconfined aquifers with respect to water table fluctuations and groundwater flow patterns, with a particular focus on wave-induced groundwater hydrodynamics. Existing analytical approaches for predicting the groundwater response to oceanic forces are summarized and evaluated to reveal their pros and cons. Although great advances have been achieved, some knowledge gaps still remain. While the influences of tide forces on coastal groundwater dynamics are generally well understood and tide-induced groundwater dynamics could be appropriately reproduced by various existing analytical or numerical models, groundwater dynamics in response to wave forces are relatively poorly understood. Accordingly, research needs with respect to groundwater dynamics are discussed and identified in this review. Many studies evaluate the wave-induced groundwater hydrodynamics based on experimental or field observations, while sophisticated theoretical approaches are still lacking to quantify the influence of various complex physical factors during wave swash events, such as capillary truncations, seepage face dynamics, and wetting front evolutions. Such knowledge gaps need to be filled in order to further advance our understanding of the coastal groundwater dynamics and, furthermore, to conduct effective and sustainable coastal water management and protection.